Global Positioning System (GPS) receivers have been used for providing position data for vehicular guidance applications. However, although certain GPS receivers with differential correction may have a general positioning error of approximately 10 centimeters (4 inches) during a majority of their operational time, an absolute positioning error of more than 50 centimeter (20 inches) is typical for five percent of their operational time. Further, GPS signals may be blocked by buildings, trees or other obstructions, which can make GPS-only navigation system unreliable in certain locations or environments. Accordingly, there is a need for supplementing or enhancing a GPS-based navigation system with one or more additional sensors to increase accuracy and robustness.